Oxygen supply system

ABSTRACT

A method of providing gas to a system which separates from a pressurized supply gas, product gas, includes conditioning the supply gas by both cooling and drying the supply gas.

DESCRIPTION OF INVENTION

This invention relates to a method of providing gas to a system whichseparates from a gas supply, product gas.

Systems are known for separating from a pressurised gas supply, such ascompressed air, product gas such as oxygen enriched gas for breathing.In one exemplary arrangement, the pressurised gas supply is hot andcompressed air bled from a gas turbine engine, and the separating systemincludes at least one, usually a plurality of, molecular sieve bedswhich include molecular sieve bed material which in a first mode ofoperation, adsorbs from the compressed air supply, non-product gas, andin a second mode of operation when the sieve bed is opened to ambientpressures, the adsorbed non-product gas is purged from the molecularsieve bed material. Thus oxygen enriched product gas is separated out ofthe supply air. Such a system is known as an OBOG (on-board oxygengenerating) system.

OBOGS are used in aircraft to produce oxygen enriched gas for breathingpurposes.

For an aircraft, weight is a critical factor for any installed system.The provision of a such system which is able to provide a breathable gasavoids the need to carry large volumes of compressed breathable gas, inheavy containers. However, OBOG efficiency depends on many factors, oneof which is the temperature of the air supply fed to it, and another ofwhich is the amount of moisture in the air supply. An OBOG operates mostefficiently to adsorb non-product gas, when the air supplied to it iswithin a certain temperature range, and because moisture in the airsupply tends to be adsorbed by the molecular sieve bed material, overlywet supply air detracts from the efficiency of operation of the OBOGtoo.

It is known in an aircraft to cool the hot compressed air supply to arelatively small extent prior to feeding the air supply to theseparation system, utilising ambient air which is used as a coolant in aheat exchanger, the ambient air typically being so-called ram air whichflows through the heat exchanger by virtue of the movement of theaircraft through the air, although on the ground, such coolant ambientair may be introduced by a fan.

Another consideration for an aircraft, particularly a military aircraftis the temperature of exhausted non-product gas, but even for a civilaircraft the exhaustion of hot non-product gas is a waste of energy.

According to one aspect of the invention we provide a method ofproviding gas to a system which separates from a pressurised supply gas,product gas the method including conditioning the supply gas by bothcooling and drying the gas.

Thus utilising the method of the invention, problems of existingsystems, particularly OBOG type systems, are at least reduced in thatthe temperature of the supply gas fed to the OBOG(S) may be controlledto be within a temperature range at which the OBOG(S) operate(s) mostefficiently, and the wet supply gas is dried. Although to condition thesupply gas will involve the provision of conditioning apparatus whichwill contribute weight, this will be counterbalanced as a smaller,lighter gas separation system than otherwise would be required, may beprovided.

In one example, the method includes cooling the supply gas sufficientlyto remove moisture from the supply gas by condensation. Thus the methodof the invention may include separating a gas supply into system gas,and supply gas, the supply gas being fed to a condenser where the supplygas is cooled by a coolant and moisture is removed from the supply gasto dry the supply gas, and passing the system gas to a cooling devicewhere the system gas is cooled, and then using the cooled system gas asthe coolant in the condenser.

The cooling device conveniently is a turbine over which the system gasis expanded. Where the gas supply is hot highly pressurised gas, such asair bled from a gas turbine engine, energy recovered from the hotpressurised gas by the turbine may be utilised by the conditioningapparatus, for example, to drive a compressor to compress and warm thesystem gas after the system gas has been used as a coolant in thecondenser.

The supply gas, after drying, may be further conditioned in a heatexchanger to bring the temperature of the supply gas to within anoptimal operating range for the downstream separating system. Suchfurther conditioning may include warming the supply gas in the heatexchanger with a warming fluid, for example with the compressed systemgas from the compressor driven by the turbine, where provided.

The method may include sensing the temperature of the supply gasdownstream of the heat exchanger, to provide an input to a controllerwhich opens and closes a valve to control the flow of the warming fluidto the heat exchanger, so that the temperature of the supply gassupplied to the separating system may be controlled.

The method may thus include compressing the expanded system gas afterusing the expanded system gas as a coolant in the condenser, warming thesupply gas after drying, in the heat exchanger with the compressedsystem gas, and then exhausting the system gas. In this way, there is aminimal wastage of energy in the gas supply and the temperature of theexhausted air need not be significantly above ambient temperature.

The method of the invention may include utilising ambient air as acoolant in a pre-cooler heat exchanger, to cool the gas supply prior toconditioning the supply gas.

According to a second aspect of the invention we provide in combinationa system which separates from supply gas, product gas, and aconditioning apparatus to cool the supply gas for use in the separatingsystem.

The system of the second aspect of the invention may have any of thefeatures of the apparatus described for use in the method of the firstaspect of the invention.

According to a third aspect of the invention we provide an aircrafthaving a combination of a system which separates from supply gas,product gas, and a conditioning apparatus to cool the supply gas for usein the separating system, according to the second aspect of theinvention.

The invention will now be described with reference to the accompanyingdrawing which an exemplary illustrative diagram of a combination of asystem which separates from supply gas, product gas, and a conditioningapparatus to cool the supply gas for use in the separating system,operable by the method of the invention.

Referring to the drawing there is shown a combination of a system 10 forseparating from a supply gas, product gas, and a conditioning apparatus12 for use in an aircraft.

A pressurised gas supply 14 is provided, which in this example is hotcompressed air bled from a gas turbine engine of the aircraft. This ispre-cooled in a pre-cooler heat exchanger 15 by a coolant which is ramair 16 which passes through the pre-cooler heat exchanger 15 due to themovement of the aircraft through the air and/or by the operation of afan. The hot compressed air supply 14 is thus cooled to some extent, butgenerally not sufficiently for optimal use in the gas separation system10 downstream.

Thus the pre-cooled but still hot and compressed air is then divided toprovide supply air along a supply duct 17, which supply air is fed tothe conditioning apparatus 12, and system air which is led along asystem air duct 18.

The system air in duct 18 is fed to a turbine 20 over which the systemair is expanded substantially to cool the system air. The cooled systemair is then fed via a duct 21, to a condenser 22 where the cooled systemair is used as a coolant to cool the supply air from duct 17 and thus tocause water present in the supply air, to be condensed out of the supplyair, so that the supply air is dried as well as cooled.

Although not shown, a downstream water separator may additionally beprovided to enable condensed water to be removed from the supply air.The cooled supply air is then fed, via an optional further heatexchanger 24 to the product gas separating system 10, which in thisexample includes a plurality of OBOGS 25, 26 (only two of which areshown for illustrative purposes) which in use, separate from the supplyair, oxygen enriched product gas for use in a downstream breathingsystem by crew/passengers of the aircraft.

The system air which was used as a coolant in the condenser 22, is fedsubsequently to a compressor 28, which for maximum efficiency is, inthis example, carried on a common shaft 29 with the turbine 20, so thatenergy recovered from the hot compressed supply air is used to drive thecompressor 28. Thus the system air is heated by being compressed beforebeing fed into a duct 30.

If after drying the supply air in the condenser 22, the temperature ofthe air is below the temperature range in which the OBOGS optimallyoperate, the temperature of the supply air may be raised in the optionalfurther heat exchanger 24, by using the compressed and thus heatedsystem air from duct 30 to warm the supply air. In order to ensure thatthe temperature of the supply air is not overly raised in the heatexchanger 24, and is raised to bring the temperature of the supply airto within the optimal temperature range for the OBOGS, a by-pass line 32may be provided for the heated compressed system air, so that the systemair or at least a proportion of it, may be exhausted to ambient at 35,without passing through the optional further heat exchanger 24.

The flow of system air along the by-pass line 32 is controlled by avalve 34 which is an electrically operated valve, operated by acontroller 38 in response to an input from a temperature sensor 39 whichis positioned to sense the temperature of the conditioned supply airjust prior to the supply air passing into the separating system 10. Thusthe valve 34 may be opened and closed by the controller, and if desiredproportionally, to ensure that the supply air is warmed only to adesired temperature in the optional further heat exchanger 24.

Various modifications may be made without departing from the scope ofthe invention. For example, although the invention has been describedparticularly for use with an oxygen concentration system 10 for anaircraft, the invention may be used for other gas systems and in otherenvironments to an aircraft. Thus the gas supply 14 need not be hot andcompressed air, but may be an ambient air supply although in this case,energy may be required to drive the turbine 20 and compressor 28 whereprovided.

Although it is preferred for there to be provided the further heatexchanger 24 to warm the dried air/gas as required, if desired analternative means for warming the supply air/gas to an optimaltemperature for use by the separating system 10 may be provided. Forexample, hot compressed gas from the gas supply 14 may be mixed with thedried supply gas, or used in a further heat exchanger to warm the supplygas instead of the compressed system air.

The features disclosed in the foregoing description, or the followingclaims, or the accompanying drawings, expressed in their specific formsor in terms of a means for performing the disclosed function, or amethod or process for attaining the disclosed result, as appropriate,may, separately, or in any combination of such features, be utilised forrealising the invention in diverse forms thereof.

1. A method of providing gas to a system which separates from apressurized supply gas, a product gas, the method comprisingconditioning the supply gas by dividing the gas supply into system gasand supply gas, feeding the supply gas to a condenser where the supplygas is cooled by a coolant and moisture is removed from the supply gasto dry the supply gas, passing the system gas to a cooling device wherethe system gas is cooled, and using the cooled system gas as the coolantin the condenser and wherein the cooled system gas is compressed afterusing the cooled system gas as a coolant in the condenser, and is usedin a heat exchanger to warm the supply gas after drying, to furthercondition the supply gas to bring the temperature of the supply gas towithin a predetermined operating range for a downstream separationsystem.
 2. A method according to claim 1 wherein the supply gas iscooled sufficiently to remove moisture from the supply gas bycondensation.
 3. A method according to claim 1 wherein the coolingdevice is a turbine over which the system gas is expanded.
 4. A methodaccording to claim 3 wherein the gas supply is hot highly pressurizedgas and energy recovered from the hot pressurized gas by the turbine isutilized by the conditioning apparatus to drive a compressor to compressand warm the system gas after the system gas has been used as a coolantin the condenser.
 5. A method according to claim 1 wherein the furtherconditioning of the supply gas comprises warming the supply gas with awarming fluid.
 6. A method according to claim 5 wherein the gas supplyis hot highly pressurized gas and energy recovered from the hotpressurized gas by the turbine is utilized by the conditioning apparatusto drive a compressor to compress and warm the system gas after thesystem gas has been used as a coolant in the condenser, and wherein thewarming fluid is compressed system gas from the compressor driven by theturbine.
 7. A method according to claim 1 which includes sensing thetemperature of the supply gas downstream of the heat exchanger, toprovide an input to a controller which opens and closes a valve inresponse, to control the flow of the warming fluid to the heatexchanger.
 8. A method according to claim 1 further comprisingexhausting the system gas from the heat exchanger.
 9. A method accordingto claim 1 wherein the method includes utilizing ambient air as acoolant in a pre-cooler heat exchanger, to cool the gas supply prior toconditioning the supply gas.
 10. A method of providing gas to a systemwhich separates from a pressurized supply gas, a product gas, the methodcomprising conditioning the supply gas by both cooling and drying thegas, wherein the supply gas is cooled sufficiently to remove moisturefrom the supply gas by condensation, and wherein a gas supply isseparated into system gas, and supply gas, and the supply gas is fed toa condenser where the supply gas is cooled by a coolant and moisture isremoved from the supply gas to dry the supply gas, and the system gas ispassed to a cooling device where the system gas is cooled, and then thecooled system gas is used as the coolant in the condenser.
 11. A methodaccording to claim 10 wherein the cooling device is a turbine over whichthe system gas is expanded.
 12. A method according to claim 11 whereinthe gas supply is hot highly pressurised gas and energy recovered fromthe hot pressurised gas by the turbine is utilised by the conditioningapparatus to drive a compressor to compress and warm the system gasafter the system gas has been used as a coolant in the condenser.
 13. Amethod according to claim 10 wherein the supply gas, after drying, isfurther conditioned in a heat exchanger to bring the temperature of thesupply gas to within an optimal operating range for the downstreamseparating system.
 14. A method according to claim 13 wherein thefurther conditioning includes warming the supply gas with a warmingfluid.
 15. A method according to claim 14 wherein the gas supply is hothighly pressurised gas and energy recovered from the hot pressurised gasby the turbine is utilised by the conditioning apparatus to drive acompressor to compress and warm the system gas after the system gas hasbeen used as a coolant in the condenser, and wherein the warming fluidis compressed system gas from the compressor driven by the turbine. 16.A method according to claim 13 which includes sensing the temperature ofthe supply gas downstream of the heat exchanger, to provide an input toa controller which opens and closes a valve in response, to control theflow of the warming fluid to the heat exchanger.
 17. A method accordingto claim 10 wherein the supply gas, after drying, is further conditionedin a heat exchanger to bring the temperature of the supply gas to withinan optimal operating range for the downstream separating system themethod including compressing the expanded system gas after using theexpanded system gas as a coolant in the condenser, warming the supplygas after drying, in the heat exchanger with the compressed system gas,and then exhausting the system gas.
 18. A method according to claim 10wherein the method includes utilizing ambient air as a coolant in apre-cooler heat exchanger, to cool the gas supply prior to conditioningthe supply gas.